Communications switching systems, particularly as used in telephony communications, typically employ a modular architecture to effect distributed processing. The architecture of a conventional telecommunications switching system generally comprises a central control unit coupled to a time division multiplexed ("TDM") switching network which in turn is communicatively coupled to a peripheral subsystem. Moreover, conventional architecture allows the systems to provide high levels of availability, even in the presence of failures of one or more components.
Typically, a central control unit is responsible for controlling the TDM switching network to process telephone calls and for directing, in general, the operation of the switching system.
The peripheral subsystem functions to provide a physical interface between the switching system and an external world consisting of subscriber lines and trunks within a telecommunications network. Examples of such known physical interfaces are DS-1, PCM-30, STS-1 and OC-3 interfaces. The peripheral subsystem usually further provides a variety of signal processing functions, including, for example, tone generation and reception, echo cancelling, support for various messaging formats and protocols, and the like.
Conventional peripheral subsystems are generally designed to fulfill generally predetermined and specific requirements for the switching system. Consequently the types, capacity and redundancy of the particular physical interfaces and signal processing functions that may be provided by the peripheral subsystem are generally predetermined and limited and may not be readily varied once the switching system has been manufactured. For example, the maximum number of subscriber lines that may be connected through a physical interface to the switching system is determined while designing the system. Similarly, the maximum ratio of signal processing resources to subscriber lines in the system is also generally predetermined. Therefore, the ability to allow for modular growth of the switching system is limited: the switching systems, capacities may not be easily varied and expanded as required. Moreover, conventional peripheral subsystem do not allow for flexible redundancy of system components in the event of component failure with means for coordinating their operation to minimize the impacts of such failure.
Additionally, in conventional subsystems many components providing signal processing and external interfacing are typically electrically interconnected to each other. Failure of a single component is thus often difficult to isolate and may affect the functioning of other components.
It is an object of the present invent ion to overcome some of the disadvantages of known communications systems.